1. Field of the Invention
The present invention relates to a data transmission system wherein a control station and tributary stations coming under the control of the control station are established among terminal connected to a transmission line in the system and regulation of transmission is all left in the charge of the control station.
2. Description of the Prior Art
As an instance of such a system the polling-addressing is well known.
In this system, the control station sequentially interrogates the tributary stations by sequentially polling or adressing the tributary stations through their connected common transmission line, and after each tributary station is polled, transmits and/or receives data in response to the answers from the polled tributary station.
Therefore, in such a case where all the tributary stations have information to be transmitted and the control station has the necessity for transmitting data to all the tributary stations, the polling or addressing by the control station with waiting or processing of a response from all the tributary stations is a wasteful thing. It is further necessary that a received transmission be judged whether it is for polling or addressing, or requesting receipt of data or transmission of data before transmission of a response or data can be conducted, and this means that the transmission line is left idle while the judgement and processing of data are being made and therefore the transmission efficiency is considerably lowered.